In the second (2G) and third generation (3G) mobile communication systems, distinct switching domains can be identified within the access networks that attach user terminals to core networks servicing the user terminals. These switching domains include the circuit-switched (CS) domain and the packet-switched (PS) domain. In the CS domain, signals are physically transported to their destination through a unique connection, whereas in the PS domain individual packets are dynamically routed to the appropriate destinations based on a destination address associated with each packet.
2G and 3G user terminals operated according to the current GSM (Global System for Mobile communication) and WCDMA (Wideband Code Division Multiple Access) standards typically access the core network via a CS access network, i.e. via the CS domain. From the CS access domain, a call will be routed to a specific service domain in the core network.
Various service domains are currently deployed for providing call services including originating, termination or mid-call services. In the past, mobile communication networks were pure CS networks. That is, the CS paradigm was underlying both the access domain and the service domain. As mobile communication networks are evolving from pure CS networks towards Internet Protocol (IP)-based networks, novel service domains are introduced. One of these novel service domains is the IP Multimedia Subsystem (IMS) currently standardised by the Third Generation Partnership Project (3GPP). The IMS is a network architecture servicing both fixed and mobile terminals which seamlessly integrates into the ubiquitous IP environment, including the Internet and other PS-based networks.
The enhanced features of the IMS service domain and of the other novel service domains are in most cases provided on a subscription basis. This means in the exemplary case of IMS that a particular call will only be routed to the IMS service domain if an IMS subscription can be determined for at least one terminal involved in the call. Otherwise, that is, if no IMS subscription can be determined, the call services will be provided in a conventional manner and typically in a CS-based service domain.
The multitude of different service domains that may be available for an individual call requires a mechanism which selectively switches on a call-by-call basis from a specific access domain to either a conventional (CS-based) service domain, to the IMS service domain, or to any other novel service domain. Depending on the current subscription status or other parameters, some call services required for or requested by a user terminal might thus be provided in one service domain, whereas other call services for this terminal might be provided in an alternative service domain. For a roaming mobile terminal, one and the same service might even be provided in different service domains when the network capabilities change with the location of the terminal. Both scenarios result in a non-uniform user experience due to the various different service domains potentially treating calls involving one and the same terminal.
In order to provide a more uniform user experience, and also to reduce the workload associated with service domain switching techniques, it would be desirable to provide a unified service domain instead of a plethora of different service domains. A corresponding solution for consistently routing calls from a CS network access through the IMS network to the IMS service domain is currently investigated by the 3GPP. The work item is called IMS Centralized Services (ICS) and aims at moving all subscribers to the IMS for a harmonization of the service environment (see 3GPP TSG SA WG2 Architecture—SA2#5, Sophia Antipolis, France, Aug. 28 to Sep. 1, 2006, Tdoc S2-063335).
The routing mechanisms required for a deployment of ICS necessitate the installation of an ICS client application that provides the underlying functionalities. Currently, two basic alternatives for the client installation are investigated. According to a first, network-centric concept, the network side is enhanced with the new routing functionalities. That is, the ICS client application is installed in the network, for example on a Mobile Switching Centre (MSC) or on an MSC server (MSC-S). As a second installation concept, the ICS client application could be placed in the terminal.
Both concepts have their merits and their drawbacks. For an early introduction, for example, it would be desirable to support ICS very quickly on the network side. Moreover, the network-centric approach scales better in the envisaged mass deployment scenario and provides ICS support also for legacy and low-end terminals. However, since there will initially be only few ICS users, a terminal-centric solution might be more resource-efficient until the unified service paradigm is generally adopted.
Accordingly, there is a need for a technique that efficiently realizes a unified service domain without renouncing on the benefits of the individual installation alternatives for the client application.